مخدش = streak

Source: http://www.marefa.org/index.php/مخدش


Mineralogy The color of the fine powder produced when a mineral is rubbed against a hard surface. Used as a distinguishing characteristic.

Source: http://www.thefreedictionary.com/streak


Almost every mineral has an inherent streak color, no matter what color the actual mineral is. For example, Calcite occurs in many different colors, shapes, and varieties. But every single variety of Calcite has a white streak. A streak is useful in distinguishing two minerals with the same color but different streak. A good example is distinguishng Gold (yellow streak), and Chalcopyrite (black streak).

Source: http://www.minerals.net/resource/property/streak.aspx